This application relates to techniques and devices for controlling light in optical waveguides such as optical fibers and other light-channeling devices. Optical waveguides include optical fibers, dielectric slab waveguide formed on a substrate, or other light-channeling devices. Such a waveguide may be used to transport light from one location to another in an optical network, within an integrated optical device, or in other settings. A waveguide may be formed by a dielectric channel that is surrounded by one or more dielectric materials with indices of refraction less than that of the dielectric channel.
For example, a typical fiber may include a fiber core, a cladding layer surrounding the fiber core, and possibly other protection layers outside the cladding layer. The refractive index of the fiber core is higher than that of the fiber cladding. Light rays, when coupled into the fiber core within a maximum angle with respect to the axis of the fiber core, can be totally reflected at the core-cladding interface and thus are spatially confined within the fiber core.
One embodiment of a wavelength-selective grating modulator includes a fiber having a fiber core and a fiber cladding layer surrounding the fiber core, and a plurality of grating trenches formed in the fiber cladding layer. The grating trenches are filled with a dielectric material that is different from the fiber cladding layer. This dielectric material is operable to change a refractive index in response to a control signal to exhibit a first refractive index substantially equal to a refractive index of the fiber cladding layer when the control signal is at a first value and to exhibit a second refractive index different from the refractive index of the cladding layer when the control signal is at a second value.
When the control signal is at the second value, a grating is present in the fiber to couple energy out of the fiber. This coupling may be used to either modulate the guided light or to attenuate the guided light. The same mechanism may be implemented in a waveguide other than a fiber, such as a planar waveguide.